Color filter arrays employed in combination with sensors to define color images or in combination with display devices to permit color images to be viewed are well known. In one illustrative system dating from the turn of the century additive primary multicolor images are formed using a panchromatically sensitized silver halide emulsion layer exposed and viewed through an array of additive primary filters. Exposure through the filter array allows silver halide to be selectively developed either in exposed or unexposed areas. A multicolor image can be viewed by projection through the developed silver and color filter array. Dufay U.S. Pat. No. 1,003,720 and Rheinberg U.S. Pat. No. 1,191,034 illustrate early versions of this filter array application. A more recently developed system of this type is illustrated by Whitmore U.S. Pat. No. 4,387,146.
Color filter arrays comprised of interlaid patterns of additive primary filters have also been employed in connection with electronic image sensors. Forming color filter arrays useful with semiconductor sensors has proven particularly challenging because of the small individual sensor areas, commonly less than 1.times.10.sup.-8 m.sup.2 in area, with areas of less than 1.times.10.sup.-10 m.sup.2 often being sought. Hartman U.S. Pat. No. 4,315,978 and Sasano et al European Pat. No. 30,476 are considered representative.
A common approach that has been taken in forming color filter arrays is to blend a conventional mordant of the type used in image transfer photography with a negative-working photoresist. Imagewise exposure of the photoresist followed by development leaves hardened photoresist and occluded mordant in exposed areas. Following development dye is imbibed into the filter elements defined by the hardened photoresist.
A discussion of image dye mordanting in image transfer photography is provided in Research Disclosure, Vol. 151, November 1976, Item 15162. Research Disclosure is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England. Campbell et al U.S. Pat. No. 3,958,995 illustrates a crosslinked mordant useful in diffusion transfer photography. Wagner et al U.K. Pat. No. 1,594,961 discloses avoiding gelatin hardening by providing hardening sites in the mordant. Helling U.S. Pat. No. 4,353,972 discloses mordants which reduce dye wandering in image transfer photography by reacting with latex polymer particles.
While the above-described approach to mordant patterning has proven workable, the filters produced have exhibited limitations, as might be expected. The mordants themselves, being in many instances borrowed from image transfer photography, have no imaging capability. The photoresists, developed primarily for use as protective, usually transient layers in semiconductor fabrication, have exhibited a variety of limitations, including significant optical density (both as initially coated and on aging) and limited solution stability. Further, the combination of both mordant and photoresist molecules in a single layer can mitigate against achieving thinner layers of satisfactory dye imparted optical densities.
Toshiba Kokai 79246/1984, based on application Ser. No. 189,081/1982, filed Oct. 29, 1982, discloses a resist composition for forming color filter elements containing 4-vinyl-N-methylpyridinium pendant groups. However, it is observed that repeating units containing these pendant groups are to be limited to 10 percent or less on a mole basis to avoid compositions poor in photosensitivity and incapable of forming an aqueous solution.
Sanada et al, "New Deep UV Dyeable Negative Resist for CCD Micro Color Filter", SPIE, Vol. 631, Advances in Resist Technology and Processing III (1986), pp. 187-191, discloses for use in forming filter elements for charge coupled devices quaternary salt terminated acrylate-glycidyl methacrylate copolymers which are crosslinked by bisazides. One difficulty of the approach is that a separate compound, the bisazide, is relied upon for crosslinking. Variances in proportions of reactants will, of course, lead to non-uniformity of results. Another fundamental difficulty is the necessity of employing very short ultraviolet (hereinafter also referred to as UV) wavelengths for crosslinking. This excludes from use the most common pattern forming exposure equipment specifically developed for fabricating semiconductor devices.